There has been considerable interest in monitoring the use of mobile terminals, such as smart phones, tablets, laptops, etc. for audience measurement and/or marketing purposes. In the area of media exposure monitoring, ancillary audio codes have shown themselves to be particularly effective in assisting media measurement entities to determine and establish media exposure data. One technique for encoding and detecting ancillary audio codes is based on Critical Band Encoding Technology (CBET), pioneered by Arbitron Inc., which is currently being used in conjunction with a special-purpose Personal People Meters (PPM™) to detect codes via ambient encoded audio.
Conventional CBET encoding and decoding is based on multiple layers, where message code symbols are encoded into separate parallel encoding layers, resulting in tens of thousands of possible codes that may be used to identify and/or characterize media. While such configurations have proven to be advantageous, thousands of codes may not be sufficient to identify and/or characterize larger media collections, which may number in the millions or billions. Accordingly, techniques are needed to be able to include much larger amounts of code data within audio. Also, techniques are needed to be able to merge or “fold” encoding layers so that more efficient coding may be enabled. Furthermore, techniques for error correction are needed to ensure that merged layer are properly encoded and/or decoded.